The invention relates to a lighting device for a motor vehicle.
Increasing use is being made nowadays in motor vehicles of lighting devices with a multiplicity of light sources which are often designed as LEDs. Various visual effects can be produced in this case by means of the use of a multiplicity of LEDs. For example, in a driving direction indicator comprising a multiplicity of juxtaposed LEDs, a wipe effect can be produced by the sequential activation of the LEDs when the driving direction indicator is switched on. It proves to be disadvantageous in lighting devices having a multiplicity of LEDs that the appearance of the lighting device is inhomogeneous because the LEDs emit in punctiform fashion, and, in addition, the LEDs must be driven individually via a multiplicity of channels.
It is therefore an object of the invention to provide a lighting device for a motor vehicle that can be used to generate light effects simply and efficiently.
The lighting device according to the invention, which is provided for a motor vehicle, is based on light guide technology. It comprises a light guide for totally reflecting guidance of light from two light sources along a light propagation axis, it being possible to couple in the light from one light source at a coupling face on one end face of the light guide, and to couple in the light from the other light source on another end face of the light guide. A decoupling face arranged along the light propagation axis is provided for decoupling light in the light guide. The decoupled light exits from the light guide in this case at an exit face arranged along the light propagation axis accompanied by cancelation of the total reflection condition.
The lighting device according to the invention is distinguished in that the light guide is designed in such a way that the light intensity distribution of the light, exiting at the exit face, of at least one light source of the two light sources and, in particular, of each of the two light sources, has a gradient in the propagation direction of the light from the respective light source. That is to say, the light intensity of the corresponding light source increases or decreases at the exit face in the propagation direction of the light.
Furthermore, a control device for the light sources is provided in such a way that the light source are activated in a prescribed switch-on time interval when the lighting device is switched on, and in this case the brightness of at least one light source, which in a preferred variant is a light source having the gradient in the light intensity distribution, is modified on the basis of a ramp and/or step profile until a prescribed brightness value is reached. The modification of the brightness in combination with the gradient in the light intensity distribution is designed in this case in such a way that the (photometric) centroid of the overall light distribution resulting at the exit face from the light intensity distributions of the two light sources travels away in the switch-on time interval along the light propagation axis to one of the coupling faces. The term of ramp and/or step profile is to be understood here and below in a wide sense. In particular, the rise and/or fall of the light distribution need not necessarily be linear in accordance with a ramp profile, but can also occur on the basis of another monotonically increasing or decreasing function. The length of the switch-on time interval can be chosen differently, and is preferably fixed in such a way that it corresponds to appropriate legal requirements, for example a maximum of 200 ms for a driving direction indicator.
With the use of light guide technology and only two light sources, the lighting device according to the invention can easily be employed to displace the photometric centroid of the light distribution, and thus to produce a light effect when the lighting device is switched on. As is described in more detail further below, the lighting device can be designed, for example, as a driving direction indicator such that the indicated driving direction is visually amplified by a wipe effect which is produced via the displacement of the photometric centroid.
In a particularly preferred embodiment, the brightness of the at least one light source increases on the basis of the ramp and/or step profile, as a result of which the effect of a traveling centroid of the overall light distribution is particularly well emphasized.
In a further refinement of the lighting device according to the invention, when the lighting device is switched on the brightness of a light source is modified on the basis of the ramp and/or step profile until the prescribed brightness value is reached, whereas the brightness of the other light source in the entire prescribed switch-on interval is set to a constant prescribed brightness value. In this variant, only one of the light source need be driven in a ramp or step fashion. Nevertheless, it is also possible for the brightness of the two light sources to be modified on the basis of a ramp and/or a step profile, as a result of which the effect of the traveling centroid of the overall light distribution can be amplified. In this case, the brightness of one light source increases in the switch-on time interval, whereas the brightness of the other light source decreases.
In a further variant of the lighting device according to the invention, the two light sources have different brightness values at the end of the switch-on time interval. In particular, the brightness value of one light source is 90% or less, and preferably 80% or less, than the brightness value of the other light source.
In a further refinement of the lighting device according to the invention, the light guide is designed as a continuous light guide section having two end faces at which the coupling faces are located. In this case, preferably, the light intensity distribution of the light, exiting at the exit face, of a respective light source decreases with increasing distance from the coupling face of the respective light source. As a result, a traveling movement of the centroid of the overall light distribution can be visualized particularly well.
In a further variant, the light guide has two separate light guide sections adjoining one another over adjacent end faces, the coupling faces being situated at end faces of the light guide sections arranged remotely from one another. Optionally, the lighting device can in this case comprise a plurality of the light guides according to the invention, it being possible, for example, for one or more of the light guides to have a continuous light guide section, and for one or more of the light guides to have two light guide sections adjoining one another.
In a preferred variant of the above embodiment of a light guide having two light guide sections, the light intensity distribution of the light, exiting at the exit face, of one light source decreases in the corresponding light guide section with increasing distance from the coupling face, whereas the light intensity distribution of the light, exiting at the exit face, of the other light source increases in the corresponding light guide section with increasing distance from the coupling face. It is preferred in this case that the control device for the light sources be designed in such a way that at the end of the switch-on time interval the overall light distribution, which results from the light intensity distributions of the two light sources on the exit face, has a continuous profile over the adjacent end faces. It is thereby suggested to a viewer that the light distribution is produced by a continuous light guide section.
In a further preferred refinement of the lighting device according to the invention, the light sources respectively comprise one or more semiconductor diodes and, in particular, one or more laser diodes.
The lighting device according to the invention can take over various functionalities in the vehicle and, in particular, be designed as a signal light and/or as a vehicle interior light and/or as a headlight. In a particularly preferred variant, the lighting device comprises a driving direction indicator. When installed in the motor vehicle, said driving direction indicator is preferably operable in such a way that the centroid of the overall light distribution, which results from the light intensity distributions of the two light sources on the exit face is displaced in the prescribed switch-on time interval to a coupling face which is situated closer to a lateral boundary of the motor vehicle adjacent to the driving direction indicator when the motor vehicle is viewed from the front or from the rear (depending on whether the driving direction indicator is arranged in the front region or rear region). A wipe effect is implemented in this way towards the turning direction of the driving direction indicator.
In one variant of the lighting device according to the invention, with a light guide comprising two separate light guide sections, the lighting device is provided for installation in a motor vehicle in such a way that the light guide sections are arranged in two different areas of the vehicle, one area of the vehicle being movable relative to the other area of the vehicle, and it being possible for the areas of the vehicle to be positioned relative to one another in such a way that the light guide sections adjoin one another over their adjacent end faces. It is possible in this way to achieve a variable arrangement of the lighting device in various vehicle parts movable relative to one another. In particular, it is possible, for example, for one light guide section to be provided in a movable tailgate, and for the other light guide section to be provided at the rear in a region fixedly adjoined thereto.
In addition to the above-described lighting device, the invention further relates to a motor vehicle which comprises one or more of the lighting devices according to the invention.
Exemplary embodiments of the invention are described below in detail with the aid of the attached figures, in which:
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.